The increased use of ethane from shale gas supplanting naphtha for steam cracking has reduced the quantity of C4 produced for petrochemical and other applications. This has driven the increased demand for C4 feedstocks derived from refineries which are increasingly being used to supplement traditional steam cracker feeds for petrochemical applications in particular. Standard adsorbents such as 13× zeolites offer insufficient capacity and poor regenerability in highly contaminated light hydrocarbon feedstocks such as those from refineries especially when olefins are present even in concentrations as low as 0.1%. Higher capacity and improved regenerability adsorbents are needed to handle these more contaminated refinery C4 feeds. Standard adsorbents suffer from poor regenerability in difficult, highly contaminated feed streams in particular where oxygenates and olefins are present. A commonly held belief in the industry is that the presence of olefins in the feed stream and particularly adsorbed olefins during regeneration are the main source of coking for adsorbents in process industry applications. However, it has been discovered that oxygenates are significant contributors to coking and potentially more detrimental than olefins. Multiple pathways for coke are present in these types of feed streams: acid catalyzed olefin oligomerization reactivity and acid or base catalyzed Aldol condensation reactivity of oxygenates, specifically carbonyls. High levels of coking are typically directly attributable to poor regenerative capacity. Therefore, an optimal adsorbent is needed to minimize the level of coking, not just toward acid catalyzed olefin oligomerization, but also toward acid and base catalyzed Aldol condensation reactions.
The adsorbent of the present invention provides 15-50% higher regenerative capacities (compared to prior art adsorbents) for a wide variety of nitrogen, oxygenate, and sulfur compounds from contaminated light hydrocarbons such as C4s and especially in olefin containing streams. In addition to higher zeolite content and higher cation density, this adsorbent offers improved access to adsorption sites through higher microporosity and larger macropores. The improved macroporosity provides additional space for carbon buildup without substantively impacting diffusivity and capacity.